This invention relates to a canister catching fuel vapor produced in a fuel system to prevent direct radiation of the fuel vapor into an atmosphere, and more particularly to such a canister having a liquid fuel reserve well formed at the bottom of a casing thereof for separating and preserving liquid fuel.
In a canister, fuel vapor produced in a fuel tank or a carburetor is caught by an adsorbent such as activated carbon while the gasified fuel components are removed from the adsorbent during the running of an engine by passing a sucked atmosphere through the adsorbent, thereby feeding the removed fuel components to the engine with the atmosphere.
Japanese Laid open Patent Application (Kokai) No. 62265460 (1987) discloses one of conventional canisters, as shown in FIG. 10. Referring to FIG. 10, a cylindrical casing 1 of the canister has a fuel reserve well 3 at the bottom. The casing interior over the fuel reserve well 3 is filled with activated carbon 2. A fuel inflow pipe 4 and a fuel outflow pipe 5 both formed into a double pipe are extended through the layer of the activated carbon 2 along the central axis of the casing 1. The fuel inflow pipe 4 has a fuel intake port 6 at the portion thereof extending into the fuel reserve well 3. The fuel outflow pipe 5 has a fuel vapor outlet 7 at the portion thereof extending into the fuel reserve well 3. The fuel vapor outlet 7 communicates with the fuel inflow pipe 4. The fuel outflow pipe 5 further has a liquid fuel outlet 8 positioned below the fuel vapor outlet 7 in the fuel reserve well 3.
A communication port 9 communicating with the atmosphere is provided at the top of the casing 1. A pipe (not shown) is connected to the upper end of the fuel inflow pipe 4 so that it is communicated to an upper interior space of a fuel tank. Another pipe (not shown) is connected to the upper end of the fuel outflow pipe 5 so that it is communicated to an air intake system of the engine.
In accordance with the above-described construction, the fuel vapor in the fuel tank flows into the fuel reserve well 3 through the fuel inflow pipe 4 and the fuel intake port 6. The fuel vapor is adsorbed into the activated carbon 2 and only the air is radiated into the atmosphere through the communication port 9.
On the other hand, the atmosphere is sucked into the casing 1 through the communication port 9 by the action of negative pressure from the engine during its running. The fuel vapor is removed from the activated carbon 2 when the atmosphere passes through the layer of the activated carbon 2. Subsequently, the atmosphere flows into the fuel outflow pipe 5 through the fuel vapor outlet 7 together with the fuel vapor, further flowing to the intake system of the engine. The liquid fuel is also fed to be reserved in the fuel reserve well 3. The reserved liquid fuel is sucked into the fuel outflow pipe 5 through the liquid fuel outlet 8 to be further sucked into the intake system together with the fuel vapor.
In the above-described conventional canister, it is difficult to control a quantity of the liquid fuel sucked from that reserved in the fuel reserve well by the action of the negative pressure from the engine. For example, a quantity of liquid fuel reserved in the fuel reserve well is all sucked in even when it is desirable to maintain at a predetermined range a ratio of the atmosphere and the fuel vapor sucked in through the fuel inflow pipe. Consequently, the density of the fuel vapor is increased too much, resulting in a problem in the fuel control.
In particular, only the liquid fuel is sucked in through the fuel outflow pipe 5 to be thereby fed to the engine immediately when a large quantity of liquid fuel is reserved in the fuel reserve well such that the liquid fuel surface rises over both of the fuel vapor outlet 7 and the liquid fuel outlet 8 in the fuel reserve well. As a result, both of the outlets 7, 8 are closed by the liquid fuel in the fuel reserve well, resulting in an excessive increase in the fuel vapor density. For example, when an automobile runs a relatively short distance, the fuel reserve well is filled with the liquid fuel such that the liquid fuel surface rises over both outlets 7, 8.